Blues and All Blacks prop Charlie Faumuina is devastated with the prognosis that his split calf would take anywhere between eight to 14 weeks to heal.

That will rule him out of the remainder of the Super Rugby season while also curtailing his opportunity to be part of the All Blacks' home series against France in the June international window.

Blues coach Sir John Kirwan said the decision to declare Faumuina injured and call up Tasman prop Sam Prattley as a replacement was done on the basis of ensuring Faumuina allowed the injury to clear up completely.

Kirwan said the end result of the injury was not known and it could be anywhere between eight to 14 weeks.

"The thing that crossed us over the line was that he needs to get this right. Our doctor said it [the injury] is more like an Achilles tendon and so we need to get him right for the rest of his career," Kirwan said. "Calves are a little bit like hamstrings for sprinters. A hard decision but we had to put the team's, and Charlie's, well-being first."

Kirwan says he had been staying awake at night wondering if Faumuina's break between his All Blacks commitments and returning to the pre-season build-up for the Blues had been a factor in the injury.

"I think it was just a case of he accelerated, if you look at the video he really put his foot down and accelerated and it was his other calf," Kirwan said. "So, did we do everything that we could? Yeah, but we couldn't see any reason bar ... next time we need to make sure he's doing a lot more sprint training."

There was a prospect that the length of break, and the work expected of players in that time, was more individualised to the positional needs and build of the players, Kirwan said. Faumuina said he accepted the rationale behind the thinking.

"Obviously everybody wants to be back in that black jersey. I think the June Tests was something we were aiming for but I think that's just going to have to be put on hold for now," Faumuina said.

It was most likely he would be available at play-offs time in the Super competition, or able to play some club rugby or in the ITM Cup for Auckland. The realisation that things had not been as expected in the healing process was when his moon boot was removed over the weekend.

"It wasn't as good as they thought it was going to be," Faumuina said.

Faumuina wasn't sure if his break between the international season and his return to the Blues environment was a factor.